As a younger athlete, I'm often told that my drive phase will lengthen as I "get stronger". What does this mean, and what are the muscles in my body that specifically allow for this? In addition to that, I am only 5ft 6in, the drive phase should be the strongest part of my race.

I question what the "drive phase" actually is. Coaches like to break up races so they can have a model, but in reality, this is what makes up a 100m race (or any sprint race, really)

Acceleration - Generally lasts 30-60m depending upon the level of the sprinter

Top Speed - More of a moment in time than a longer phase, maximal velocity is reached for a very short time (10m or less) before you start decelerating

Deceleration - This is what you are trying to minimize as much as possible via speed endurance work.

How will getting stronger help your acceleration? Well if you produce more force, you can increase your propulsive impulse each step and thus you will go further each step. Velocity is Meters/Second, so the further you go in the same amount of time, the faster you are sprinting. Its reasonable to say that less experienced athletes will see a greater improvement in acceleration from getting stronger, while more experienced athletes may not see much of a change or they could possibly get slower (if they did too much slow, grinding max strength lifts).

I see. After building a certain degree of max strength, perhaps 2.5x-3x BW squat, do you think an athlete should move onto things like Olympic lifts/ explosive lifts like jump squats to further improve their drive phase?

Also, what is it that allows pros to come out at a lower angle and stay there for a longer period of time? Is it due to things like core strength, allowing them to stay low?